'68 GMC - New guy with questions

[ZEPPELIN]

I picked up this sweet '68 GMC about 10 days ago. It's currently my daily driver, and I'm loving the attention it gets! It has a TBI 350 out of a '91 with a TH400 trans. I believe the rear end is out of the same vehicle the engine came from, but I'm not sure how to identify it. Everything on the truck works and it runs strong. The only issue I've had so far is this: when the engine is cold, it'll start up on the 3rd or 4th crank every time and run great. Once it's warm, though, whether it's been driven 1 mile or 100, when I try to restart it, it takes about 10-15 seconds of cranking before it fires. Then the first few times I push the gas after the restart, it coughs and sputters a bit before taking off. After that it's fine. It always has a fairly rich exhaust smell, too. It does run well, and it still starts every time, so I'm hesitant to screw with it, but where would you guys start if you wanted to fix these problems? Thanks